ArcGIS Online Add WFS Error

[LeeButler]

I have been sent the following WFS URL (http://demo.kaarbontech.co.uk/wfs) and am trying to add the data to ArcGIS Online.  When I add a new WFS OGC Web Service to AGOL I get the following error?

Any ideas what I am doing wrong when trying to add this data?

Thanks

Lee

[DouglasCochran]

When I go to:  http://demo.kaarbontech.co.uk/wfs 

It requires sign-in authorization.  Could that be the problem for you as well?

[LeeButler]

The wfs service does require authorisation however when I try and add the service to ArcGIS Online I immediately get the above error and am not prompted to enter a username and password to access the service.  I can share the login details with you privately if that would help?

Thanks

Lee